Professor Thomas' research is focused on the study of the biology and clinical use of human dendritic cells in autoimmune disease. It has explored basic mechanisms of immunity and dendritic cell function in autoimmune disease.
She received her MBBS in 1984, and then trained in Perth as a rheumatologist. She commenced a research fellowship with Peter Lipsky at Southwestern Medical Center, University of Texas in 1990, where she first identified and characterised human circulating dendritic cell precursors. In 2020 she was awarded Member of the Order of Australia.Her research is focussed on the study of autoimmune disease and restoration of tolerance. Through this work, she developed and tested the first rheumatoid arthritis vaccine. She has also contributed major insights into the pathogenesis of spondyloarthropathy and autoimmune diabetes, leading to the development of disease biomarkers and innovative immunotherapies. With Uniquest, Ranjeny founded Dendright, which developed antigen-specific (personalised) immunotherapy and companion biomarkers to prevent and treat rheumatoid arthritis. She is funded by the Juvenile Diabetes Research Foundation and the Helmsley Foundation to develop antigen-specific immunotherapy for children with type 1 diabetes.